Saint Mary's Faculty Articles and Other Workshttp://library2.smu.ca:80/handle/01/218802018-02-21T19:42:15Z2018-02-21T19:42:15ZHybrid cosmological simulations with stream velocitiesRichardson, Mark L. A.Scannapieco, EvanThacker, Robert John, 1970-http://library2.smu.ca:80/handle/01/272832018-02-21T18:00:25Z2013-01-01T00:00:00ZHybrid cosmological simulations with stream velocities
In the early universe, substantial relative “stream” velocities between the gas and dark matter arise due to radiation pressure and persist after recombination. To assess the impact of these velocities on high-redshift structure formation, we carry out a suite of high-resolution adaptive mesh refinement (AMR) cosmological simulations, which use smoothed particle hydrodynamic data sets as initial conditions, converted using a new tool developed for this work. These simulations resolve structures with masses as small as a few 100 M[circled dot], and we focus on the 10[superscript 6] M[circled dot] “mini-halos” in which the first stars formed. At z ≈ 17, the presence of stream velocities has only a minor effect on the number density of halos below 10[superscript 6] M[circled dot], but it greatly suppresses gas accretion onto all halos and the dark matter structures around them. Stream velocities lead to significantly lower halo gas fractions, especially for ≈10[superscript 5] M[circled dot] objects, an effect that is likely to depend on the orientation of a halo’s accretion lanes. This reduction in gas density leads to colder, more compact radial profiles, and it substantially delays the redshift of collapse of the largest halos, leading to delayed star formation and possibly delayed reionization. These many differences suggest that future simulations of early cosmological structure formation should include stream velocities to properly predict gas evolution, star formation, and the epoch of reionization.
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2013-01-01T00:00:00Zgamma Doradus pulsation in two pre-main sequence stars discovered by CoRoTZwintz, K.Fossati, L.Ryabchikova, T.Kaiser, A.Gruberbauer, MichaelBarnes, T. G.Baglin, A.Chaintreuil, S.http://library2.smu.ca:80/handle/01/272822018-02-21T16:00:25Z2013-01-01T00:00:00Zgamma Doradus pulsation in two pre-main sequence stars discovered by CoRoT
Context. Pulsations in pre-main sequence stars have been discovered several times within the last years. But nearly all of these pulsators are of [delta] Scuti-type. [gamma] Doradus-type pulsation in young stars has been predicted by theory, but lack observational evidence. Aims. We present the investigation of variability caused by rotation and ([gamma] Doradus-type) pulsation in two pre-main sequence members of the young open cluster NGC 2264 using high-precision time series photometry from the CoRoT satellite and dedicated high-resolution spectroscopy. Methods. The variability found using the CoRoT data was combined with the fundamental parameters and chemical abundances derived from high-resolution spectroscopy, obtained at the Mc Donald Observatory, to discuss the presence of pulsation and rotation in the two NGC2264 cluster members. Time series photometry of NGC2264 VAS 20 and NGC2264 VAS 87 was obtained by the
CoRoT satellite during the dedicated short run SRa01 in March 2008. NGC2264 VAS 87 was re-observed by CoRoT during the short run SRa05 in December 2011 and January 2012. Frequency analysis was conducted using Period04 and SigSpec. The spectral analysis was performed using equivalent widths and spectral synthesis. Results. The frequency analysis yielded ten (NGC2264 VAS 20) and fourteen (NGC2264 VAS 87) intrinsic frequencies in the range from 0 to 1.5 d[superscript −1], which are attributed to be caused by a combination of rotation and pulsation. The effective temperatures were derived to be 6380 [plus or minus] 150 K for NGC2264 VAS 20 and 6220 [plus or minus] 150 K for NGC2264 VAS 87. Membership of the two stars to the cluster is confirmed independently using X-ray fluxes, radial velocity measurements, and proper motions available in the literature. The derived lithium abundances of log n(Li) = 3.34 and 3.54 for NGC 2264 VAS 20 and NGC2264 VAS 87 agree with the lithium abundance for other stars in NGC2264 of similar Teff reported in the literature. Conclusions. We conclude that the two objects are members of NGC 2264 and therefore are in their pre-main sequence evolutionary stage. Their variability is attributed to be caused by rotation and g-mode pulsation rather than rotation only. Assuming that part of their variability is caused by pulsation, these two stars might be the first pre-main sequence [gamma] Doradus candidates.
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2013-01-01T00:00:00ZOn the form of the Spitzer Leavitt Law and its dependence on metallicityMajaess, Daniel J.Turner, David Gerald, 1945-Gieren, W.http://library2.smu.ca:80/handle/01/272812018-02-21T15:08:43Z2013-01-01T00:00:00ZOn the form of the Spitzer Leavitt Law and its dependence on metallicity
The form and metallicity dependence of Spitzer mid-infrared Cepheid relations are a source of debate. Consequently, Spitzer 3.6 and 4.5 [mu] m period–magnitude and period–color diagrams were re-examined via robust routines, thus providing an alternative interpretation to consider. The relations (nearly mean-magnitude) appear nonlinear over an extensive baseline (0.45 < log P[subscript 0] < 2.0), particularly the period–color trend, which to first order follows constant (3.6–4.5) color for shorter-period Cepheids and may transition into a bluer convex trough at longer periods. The period–magnitude functions can be described by polynomials (e.g., [3.6 mu m] = K[subscript 0] − (3.071 [plus or minus] 0.059) log P[subscript 0] − (0.120 [plus or minus] 0.032) log P[subscript 0 superscript 2]), and Cepheid distances computed using 3.6 and 4.5 [mu] m relations agree with each other and the latter provides a first-order consistency check (CO sampled at 4.5 [mu] m does not seriously compromise those distances). The period–magnitude relations appear relatively insensitive to metallicity variations ([Fe/H] ∼ 0 to −0.75 |[gamma] | < 0.1 mag dex[superscript −1]), a conclusion inferred partly from comparing galaxy distances established from those relations and NED-D (n > 700), yet a solid conclusion awaits comprehensive mid-infrared observations for metal-poor Cepheids in IC 1613 ([Fe/H] ∼ −1). The Cepheid-based distances were corrected for dust obscuration using a new ratio (i.e., A[subscript 3.6]/E[subscript B−V] = 0.18 [plus or minus] 0.06) deduced from GLIMPSE (Spitzer) data.
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2013-01-01T00:00:00ZRegular frequency patterns in the young [delta] Scuti star HD 261711 observed by the CoRoT and MOST satellitesZwintz, K.Fossati, L.Guenther, David B.Ryabchikova, T.Baglin, A.Themessl, N.Barnes, T. G.Matthews, J. M.Auvergne, M.Bohlender, D.http://library2.smu.ca:80/handle/01/272802018-02-21T14:43:51Z2013-01-01T00:00:00ZRegular frequency patterns in the young [delta] Scuti star HD 261711 observed by the CoRoT and MOST satellites
Context. The internal structure of pre-main-sequence (PMS) stars is poorly constrained at present. This could change significantly through high-quality asteroseismological observations of a sample of such stars. Aims. We concentrate on an asteroseismological study of HD261711, a rather hot [delta] Scuti-type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD261711 was discovered to be a PMS [delta] Scuti star using the time series photometry obtained by the MOST satellite in 2006. Methods. High-precision, time-series photometry of HD261711 was obtained by the MOST and CoRoT satellites in four separate new observing runs that are put into context with the star’s fundamental atmospheric parameters obtained from spectroscopy. Frequency Analysis was performed using Period04. The spectral analysis was performed using equivalent widths and spectral synthesis. Results. With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the [delta] Scuti variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new [delta] Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group were determined and are related to l = 0 and l = 1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature (T[subscript eff]) was derived to be 8600 [plus or minus] 200 K, log g is 4.1 [plus or minus] 0.2, and the projected rotational velocity (υ sin i) is 53 [plus or minus] 1 km s[superscript −1]. Using our T[subscript eff] value and the radius of 1.8 [plus or minus] 0.5 R[circled dot] derived from spectral energy distribution (SED) fitting, we get a luminosity log L/L[circled dot] of 1.20 [plus or minus] 0.14 which agrees well to the seismologically determined values of 1.65 R[circled dot] and, hence, a log L/L[circled dot] of 1.13. The radial velocity of 14 [plus or minus] 2 km s[superscript −1] we derived for HD261711, confirms the star’s membership to NGC2264. Conclusions. Our asteroseismic models suggest that HD261711 is a [delta] Scuti-type star close to the zero-age main sequence (ZAMS)
with a mass of 1.8 to 1.9 M[circled dot]. With an age of about 10 million years derived from asteroseismology, the star is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning. The observed splittings about the l = 0 and 1 parent modes may be an artifact of the Fourier derived spectrum of frequencies with varying amplitudes.
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2013-01-01T00:00:00ZThe asymmetric drift, the local standard of rest, and implications from RAVE dataGolubov, O.Just, A.Bienayme, O.Bland-Hawthorn, J.Gibson, Brad K.Grebel, E. K.Munari, U.Navarro, J. F.Parker, Q.Seabroke, G.http://library2.smu.ca:80/handle/01/272792018-02-20T20:58:00Z2013-09-01T00:00:00ZThe asymmetric drift, the local standard of rest, and implications from RAVE data
Context. The determination of the local standard of rest (LSR), which corresponds to the measurement of the peculiar motion of the Sun based on the derivation of the asymmetric drift of stellar populations, is still a matter of debate. The classical value of the tangential peculiar motion of the Sun with respect to the LSR was challenged in recent years, claiming a significantly larger value.
Aims. We present an improved Jeans analysis, which allows a better interpretation of the measured kinematics of stellar populations in the Milky Way disc. We show that the Radial Velocity Experiment (RAVE) sample of dwarf stars is an excellent data set to derive tighter boundary conditions to chemodynamical evolution models of the extended solar neighbourhood. Methods. We propose an improved version of the Strömberg relation with the radial scalelengths as the only unknown.We redetermine the asymmetric drift and the LSR for dwarf stars based on RAVE data. Additionally, we discuss the impact of adopting a different LSR value on the individual scalelengths of the subpopulations.
Results. Binning RAVE stars in metallicity reveals a bigger asymmetric drift (corresponding to a smaller radial scalelength) for more metal-rich populations. With the standard assumption of velocity-dispersion independent radial scalelengths in each metallicity bin, we redetermine the LSR. The new Strömberg equation yields a joint LSR value of V[subscript circled dot] = 3.06 [plus or minus] 0.68 km s[superscript −1], which is even smaller than the classical value based on Hipparcos data. The corresponding radial scalelength increases from 1.6 kpc for the metal-rich bin to 2.9 kpc for the metal-poor bin, with a trend of an even larger scalelength for young metal-poor stars. When adopting the recent Schönrich value of V[subscript circled dot] = 12.24 km s[superscript −1] for the LSR, the new Strömberg equation yields much larger individual radial scalelengths of the RAVE subpopulations, which seem unphysical in part. Conclusions. The new Strömberg equation allows a cleaner interpretation of the kinematic data of disc stars in terms of radial scalelengths. Lifting the LSR value by a few km s[superscript−1] compared to the classical value results in strongly increased radial scalelengths with a trend of smaller values for larger velocity dispersions.
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2013-09-01T00:00:00ZThe distance to the young open cluster Westerlund 2Carraro, G.Turner, David Gerald, 1945-Majaess, Daniel J.Baume, G.http://library2.smu.ca:80/handle/01/272782018-02-20T20:27:50Z2013-07-01T00:00:00ZThe distance to the young open cluster Westerlund 2
A new X-ray, UBVRI[subscript c], and JHKs study of the young cluster Westerlund 2 was undertaken to resolve discrepancies tied to the cluster’s distance. Existing spectroscopic observations for bright cluster members and new multi-band photometry imply a reddening relation toward Westerlund 2 described by E[subscript U−B]/E[subscript B−V] = 0.63 + 0.02 E[subscript B−V]. Variable-extinction analyses for Westerlund 2 and nearby IC 2581 based upon spectroscopic distance moduli and ZAMS fitting yield values of R[subscript V] = A[subscript V]/E[subscript B−V] = 3.88 [plus or minus] 0.18 and 3.77 [plus or minus] 0.19, respectively, and confirm prior assertions that anomalous interstellar extinction is widespread throughout Carina. The results were confirmed by applying the color-difference method to UBVRI[subscript c]JHK[subscript s] data for 19 spectroscopically observed cluster members, yielding RV = 3.85 [plus or minus] 0.07. The derived distance to Westerlund 2 of d = 2.85 [plus or minus] 0.43 kpc places the cluster on the far side of the Carina spiral arm. The cluster’s age is no more than [tau] [approximately equal to] 2 × 10[superscript 6] yr as inferred from the cluster’s brightest stars and an X-ray (Chandra) cleaned analysis of its pre-main-sequence demographic. Four Wolf-Rayet stars in the cluster core and surrounding corona (WR20a, WR20b, WR20c, and WR20aa) are very likely cluster members, and their inferred luminosities are consistent with those of other late-WN stars in open clusters. The color–magnitude diagram for Westerlund 2 also displays a gap at spectral type B0.5 V with associated color spread at higher and lower absolute magnitudes that might be linked to close binary mergers. These features, in conjunction with the evidence for mass loss from the WR stars, may help to explain the high flux of [gamma]-rays, cosmic rays, and X-rays from the direction toward Westerlund 2.
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2013-07-01T00:00:00ZThe long-term binary system VV CepPollmann, EBennett, Philip Desmond, 1952-Hopkins, J. L.http://library2.smu.ca:80/handle/01/272772018-02-20T13:21:11Z2016-01-16T00:00:00ZThe long-term binary system VV Cep
VV Cep is an eclipsing binary with a period of about 20.4 years that is comprised of an M2Iab primary star and an early B secondary star. A preliminary orbit was announced in 1933 by Harper & Christie (1936), and McLaughlin (1934) described the behaviour of the wide emission lines of Hydrogen and those of ionized CaII, the H & K lines, which were divided by sharp absorption and shifted in velocity, and presented the V/R (violet to red component) ratio for the Hydrogen Balmer lines. In October 1936, McLauglin (1936) announced that the hot star in VV Cep had been eclipsed, establishing the system as an eclipsing binary. Goedicke (1939a,b) carried out the first detailed spectroscopic analysis of this system. Wright (1977) inferred the existence of intermittent mass transfer and an H[alpha] emitting disk. Kawabata et al. (1981) and Moellenhoff & Schaifers (1978, 1981) further described what appeared to be an accretion disk around the B star. The dimension of the disk around the Be star was determined by Peery (1966) to be less than 1/18 of the diameter of the M supergiant’s photosphere, and according to investigations of Hutchings & Wright (1971) it is not spherically symmetrical, but rather is more dense in the direction of the stellar equator, as in the case of a normal Be star. This seems to be quite logical in view of the remarkable stream of gas in this system. Long-term monitoring of the intensity variations of the V and R emission peaks (the so-called V/R ratio) delivers important information about the peak strength as measure or the mass and/or density of the gas in the disk, expressed as equivalent width (EW) of the emission, and the direction of movement of the corresponding gas region within the disk (Figure 1). The violet and the red (V and R) components into which the emission line of the VV Cep spectrum is split can be linked to the radiation of the gas disk around the Be star. Due to its counterclockwise rotation around the central star, in relation to the line of sight of the observer, it results in a blueshift by moving towards the observer (V component) and a redshift by moving away (R component) from the observer.
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2016-01-16T00:00:00ZMarginal contrasts and the contrastivist hypothesisHall, Daniel CurrieHall, Kathleen Curriehttp://library2.smu.ca:80/handle/01/272762018-02-20T14:26:11Z2016-12-06T00:00:00ZMarginal contrasts and the contrastivist hypothesis
The Contrastivist Hypothesis (CH; Hall 2007; Dresher 2009) holds that the only features that can be phonologically active in any language are those that serve to distinguish phonemes, which presupposes that phonemic status is categorical. Many researchers, however, demonstrate the existence of gradient relations. For instance, Hall (2009) quantifies these using the information-theoretic measure of entropy (unpredictability of distribution) and shows that a pair of sounds may have an entropy between 0 (totally predictable) and 1 (totally unpredictable). We argue that the existence of such intermediate degrees of contrastiveness does not make the CH untenable, but rather offers insight into contrastive hierarchies. The existence of a continuum does not preclude categorical distinctions: a categorical line can be drawn between zero entropy (entirely predictable, and thus by the CH phonologically inactive) and non-zero entropy (at least partially contrastive, and thus potentially phonologically active). But this does not mean that intermediate degrees of surface contrastiveness are entirely irrelevant to the CH; rather, we argue, they can shed light on how deeply ingrained a phonemic distinction is in the phonological system. As an example, we provide a case study from Pulaar [ATR] harmony, which has previously been claimed to be problematic for the CH.
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2016-12-06T00:00:00ZnIFTy galaxy cluster simulations – I. Dark matter and non-radiative modelsSembolini, FedericoYepes, GustavoPearce, Frazer R.Knebe, AlexanderKay, Scott T.Power, ChrisCui, WeiguangBeck, Alexander M.Borgani, StefanoVecchia, Claudio DallaThacker, Robert John, 1970-http://library2.smu.ca:80/handle/01/272742018-02-19T23:53:21Z2016-04-21T00:00:00ZnIFTy galaxy cluster simulations – I. Dark matter and non-radiative models
We have simulated the formation of a galaxy cluster in a [lambda] cold dark matter universe using 13 different codes modelling only gravity and non-radiative hydrodynamics (RAMSES, ART, AREPO, HYDRA and nine incarnations of GADGET). This range of codes includes particle-based, moving and fixed mesh codes as well as both Eulerian and Lagrangian fluid schemes. The various GADGET implementations span classic and modern smoothed particle hydrodynamics (SPH) schemes. The goal of this comparison is to assess the reliability of cosmological hydrodynamical simulations of clusters in the simplest astrophysically relevant case, that in which the gas is assumed to be non-radiative. We compare images of the cluster at z = 0, global properties such as mass and radial profiles of various dynamical and thermodynamical quantities. The underlying gravitational framework can be aligned very accurately for all the codes allowing a detailed investigation of the differences that develop due to the various gas physics implementations employed. As expected, the mesh-based codes RAMSES, ART and AREPO form extended entropy cores in the gas with rising central gas temperatures. Those codes employing classic SPH schemes show falling entropy profiles all the way into the very centre with correspondingly rising density profiles and central temperature inversions. We show that methods with modern SPH schemes that allow entropy mixing span the range between these two extremes and the latest SPH variants produce gas entropy profiles that are essentially indistinguishable from those obtained with grid-based methods.
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2016-04-21T00:00:00ZOrbitally modulated photoexcited Si I emission in the eclipsing composite-spectrum binary [zeta] AurigaeHarper, G. M.Griffin, R. E. M.Bennett, Philip Desmond, 1952-O’Riain, N.http://library2.smu.ca:80/handle/01/272732018-02-20T00:20:05Z2016-02-21T00:00:00ZOrbitally modulated photoexcited Si I emission in the eclipsing composite-spectrum binary [zeta] Aurigae
We examine the little-known phenomenon of orbitally modulated Si I emission at [lambda] 3905.523 [angstrom] and [lambda] 4102.936 [angstrom] in composite-spectrum binaries, with specific reference to [zeta] Aurigae (K4 Ib + B5 V). The emission is detected in the isolated spectrum of the B-type dwarf secondary, and while [lambda] 4102 [angstrom] is heavily blended with H[delta], [lambda] 3905 [angstrom] falls in the B-star’s featureless continuum. The narrowness of the emission (v [subscript turb] [similar or equal to] 6 km s[superscript-1]) demonstrates that it originates in the upper photosphere or deep chromosphere of the K star primary. We propose that photoexcitation by the hot star’s UV continuum, followed by recombination and cascades, leads to resonant scattering and subsequent pumping of lower opacity transitions in the singlet and triplet systems of Si I. This process channels the UV continuum into select narrow emission lines. We have also identified weaker photoexcited emission of Fe II at [lambda] 3938.289 [angstrom]. The strengths, positions, and widths of the [lambda] 3905 [angstrom] emission line vary with orbital phase owing to changes in the dilution of the irradiating flux and in the geometrical aspect of the irradiated hemisphere. Utilizing the inherent spatial resolution provided by the illuminated patch, and assuming that the K star is spherical with isotropic emission, yields vsin i [similar to] 5.7 km s[superscript-1]. Evidence of tidal distortion was deduced from the timing of the rapidly rising phase of the emission just after periastron. Increasing the diagnostic potential requires radiative transfer modelling of the formation and centre-to-limb variation of the emission.
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2016-02-21T00:00:00Z